fiend vs evil spirit

fiend and evil spirit both are nouns.

Word	Noun	Adjective	Verb	Adverb
fiend	Yes	No	No	No
evil spirit	Yes	No	No	No

As nouns, evil spirit is a hypernym of fiend; that is, evil spirit is a word with a broader meaning than fiend:

fiend (noun)	evil spirit (noun)
a cruel wicked and inhuman person	a spirit tending to cause harm
a person motivated by irrational enthusiasm (as for a cause)
an evil supernatural being